Clustering of substance use and sexual risk behaviour in adolescence: analysis of two cohort studies.

Thus, increases in mean numbers of late adolescent risk behaviours were greater among girls (0.75 vs 1.56; age and social class adjusted p<0.001) than boys (1.50 vs 1.93; adjusted p=0.048); the cohort-by-gender interaction was highly significant (adjusted p<0.001) (web table 1).

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